Compared to regular battery and rechargeable battery, solar cells are more environment-friendly. Present solar panels are usually composed of five layers that are pressed and bonded together. From top to bottom the five layers are tempered glass, ethylene vinyl acetate (EVA), solar cell, EVA, backplane. Then a stainless steel frame can be added to hold the panels. Because such solar panels have tempered glass, backplane and steel frame, they are heavy and bulky and usually suitable for outdoor uses, such as rooftop and roadside applications.
Currently there are three types of solar-powered chargers on the market, and they have different charging methods. One type of charger can charge non-Apple® devices normally. The charging current decreases when the amount of light shining on the solar panels decreases, and vice versa. However, Apple® devices have a built-in automatic self-protection mechanism which prevents this type of charger from charging Apple® devices normally when the amount of light changes. In particular, the charging current decreases when the amount of light decreases, but the charging current will not recover when the amount of light increases.
Another type of charger has a built-in voltage regulator. When it is charging Apple® devices, the charging current decreases as the amount of light decreases. When the amount of light increases, the voltage regulator can be automatically reset and the charging current recovers. However, if the amount of light is not stable, the voltage regulator can turn on and off frequently which leads to a bad user experience.
The other type of charger cannot distinguish between Apple® devices and non-Apple® devices at the USB interface. Thus, users have to choose the corresponding charging ports for their devices. When it is charging Apple® devices and the amount of light changes, it can automatically reset after a three minutes delay time, which is not user-friendly.
Therefore there is a need for an adaptive solar charging system.